The majority of electronic equipment produced presently, and in particular computers, communication systems, military surveillance equipment, stereo and home entertainment equipment, televisions and other appliances include miniaturized components to perform new high speed functions and electrical interconnections which according to the materials from which they are made or their mere size are very susceptible to stray electrical energy created by electromagnetic interference or voltage transients occurring on electrical lines. Voltage transients can severely damage or destroy such micro-electronic components or contacts thereby rendering the electronic equipment inoperative, and requiring extensive repair and/or replacement at great cost.
Electrical interference in the form of EMI or RFI can be induced into electrical lines from such sources as radio broadcast antennas or other electromagnetic wave generators. EMI can also be generated from the electrical circuit which is desired to be shielded from EMI. Differential and common mode currents are typically generated in cables and on circuit board tracks. In many cases fields radiate from these conductors which act as antennas. Controlling these conducted/radiated emissions is necessary to prevent interference with other circuitry or other parts of the circuit generating or sensitive to the unwanted noise. Other sources of interference are generated from equipment coupled to the electrical lines, such as computers, switching power supplies and a variety of other systems, which may generate significant interference which is desired to be eliminated to meet international emission and/or susceptibility requirements.
Transient voltages occurring on electrical lines can be induced by lightning which produces extremely large potentials in a very short time. In a similar manner, nuclear electromagnetic pulses (EMP) generate even larger voltage spikes with faster rise time pulses over a broad frequency range which are detrimental to most electronic devices. Other sources of large voltage transients are found to be associated with voltage surges occurring upon the switching off or on of some electronic power equipment as well as ground loop interference caused by varying ground potentials. Existing protection devices, primarily due to their architecture and basic materials, do not provide adequate protection in a single integrated package.
Based upon the known phenomenon of electromagnetic emissions and transient voltage surges a variety of filter and surge suppression circuit configurations have been designed as is evident from the prior art. A detailed description of the various inventions in the prior art is disclosed in U.S. Pat. No. 5,142,430, herein incorporated by reference.
The '430 patent itself is directed to power line filter and surge protection circuit components and the circuits in which they are used to form a protective device for electrical equipment. The circuit components comprise wafers or disks of material having desired electrical properties such as varistor or capacitor characteristics. The disks are provided with electrode patterns and insulating bands on surfaces thereof which coact with apertures formed therein so as to electrically connect the components to electrical conductors of a system easily and effectively. These electrode patterns act in conjunction with one another to form common electrodes with the material interposed there between. The '430 patent was primarily directed toward filtering paired lines. The present invention improves on the paired line concept by refining and adapting the concept for use with low voltage low current data communication lines as well as arrangements directed towards high voltage industrial and home applications such as three phase power lines, electric motor noise filtering, LANs and other computer devices.
Therefore, in light of the foregoing deficiencies in the prior art, the applicant's invention is herein presented.